1. Field of the Invention
The present invention relates to an optical disc.
2. Description of the Related Art
Generally, optical discs being recording mediums for recording information such as video data, audio data, etc. are widely used. In addition to commercialized CDs (Compact Discs) as the optical discs, read-only optical discs such as a CD-ROM (Compact Disc-Read Only Memory), a DVD-ROM (Digital Versatile Disc-Read Only Memory), etc., write-once optical discs such as a CD-R (Compact Disc-Recordable), a DVD-R (Digital Versatile Disc-Recordable), etc., and rewritable optical discs such as a CD-RW (CD-Rewritable), a DVD-RAM (Compact Disc-Random Access Memory), a DVD-RW (DVD-Rewritable), etc. are currently supplied and developed.
Identification information containing address information, etc. is written on the rewritable optical disc so that data is written in a desired write location. As shown in FIG. 1, a signal track 10 of a land and a signal track 12 of a groove are arranged on the optical disc of the CD-R. The identification information containing the address information is pre-formatted on the signal track 12 of the groove wobbled according to a frequency-modulated carrier signal.
The address information is read from a wobble signal of the signal track 12 of the wobbled groove as described above, and data can be recorded on a specific location of the optical disc based on the read address information.
However, because the address information is recorded on only the signal track of the groove in a conventional optical disc, recording capacity for the address information is limited.
On the other hand, as an optical disc capable of recording the address information on both signal tracks of the land and the groove, an optical disc shown in FIG. 2, e.g., the DVD-RAM is known. The optical disc includes header fields having pre-pit arrays 14 in which identification information containing the address is recorded, and record fields having signal tracks 10 and 12 of the land and the groove wobbled in phase.
However, because data that a user desires to record cannot be recorded on the header fields made up of the pre-pit arrays 14 in the above-described optical disc, recording capacity for user data is limited.
On the other hand, a method for maximizing recording capacity by allowing the address information as wobble signals to be recorded on both signal tracks of the land and the groove is proposed. The method will be described in detail.
First, referring to FIG. 3, signal tracks 20 and 22 of a land and a groove are formed, and the signal tracks 20 and 22 are formed, in parallel, in a spiral form from an innermost circle to an outermost circle. As shown in FIG. 4, the signal tracks 20 and 22 can be alternately arranged for every rotation from the innermost circle to the outermost circle so that a spiral-shaped signal track can be formed.
On the other hand, the signal tracks 20 and 22 of lands and grooves include a pair of sides, wobbled in phase, corresponding to an in-phase wobbled portion 24A and another pair of sides, wobbled in anti-phase, an anti-phase wobbled portion 24B, wherein the pairs are alternately formed. The in-phase wobbled portion 24A and the anti-phase wobbled portion 24B are alternated in a width direction of the signal track.
Further, hatched in-phase wobbled portions 24A have the identification information containing the address information, etc. pre-formatted on both sides of each portion 24A. The identification information is wobbled according to a frequency-modulated carrier signal. The in-phase wobbled portions 24A and the anti-phase wobbled portions 24B are alternately arranged in traveling and width directions of the signal tracks 20 and 22. Both sides of each anti-phase wobbled portion 24B are wobbled in different phases.
Accordingly, the address information is obtained from a wobble signal on the in-phase wobbled portion 24A. For example, as shown in FIG. 3, where an in-phase wobbled portion and an anti-phase wobbled portion are used as one information-recording unit, i.e., a frame, the address information is read from in-phase wobbled portions located in the front and back of an anti-phase wobbled portion. On the basis of the read address information, user data can be recorded on the information-recording unit.
In a recording medium based on the above-described manner, information can be recorded on all the signal tracks of the lands and the grooves. Accordingly, all recordable portions of the recording medium can be utilized.
However, in a method for recording a wobble signal on each of the signal tracks of the land and the groove, one period signal is allocated to one bit of the address information. Because the signal is phase-modulated and the phase-modulated signal is recorded, a valid address or an invalid address can be detected according to a tracking state of an optical pickup.
For example, as shown in FIG. 5, where beam spots of the optical pickup are appropriately arranged on both sides of a signal track of a groove, phases of wobble signals formed on both sides of a signal track of a groove are in phase, and a push-pull signal having an amplified signal level of a waveform corresponding to each wobble signal is outputted. A digital wobble signal is detected as a sliced push-pull signal, and a reproduction RF (Radio Frequency) signal of a zero level is outputted. However, where the beam spots of the optical pickup are not appropriately arranged on both sides of a signal track of a land, phases of the wobble signals formed on both sides of a signal track of a land may be in anti-phase. In this case, since consecutively repeated zero-level sections exist in the push-pull signal, a digital wobble signal sliced to a predetermined level also has the consecutively repeated zero-level sections, resulting in generating a signal having an irregular period. Accordingly, there are problems in that performance of a PLL (Phase-Locked Loop) is significantly degraded and a noise is generated in a reproduction RF signal.